No Start: Bad starter solenoid, bad wiring, or a defective anti-theft system?

Question

The vehicle is a 2010 Fiat Ducato (x250) 2.3L Turbo Diesel with an old third party Ituran anti-theft system.

There are two codes

• U1602 CAN Line, Bus Off in the Instrument Cluster - intermittent
• D602 CAN Line Error, Bus Off in the Body Computer.

The engine does not turn over at all. Battery full and verified as good. There is a small 300ma parasitic draw which drops to 100ma when the fuse for the security system is pulled. There is also a history of hard starting when the engine is cold. The starter seems to have been replaced once already.

Start Attempt 1 - Measurements taken while cranking

• VDrop across the engine ground strap of 0.5 volts.
• B+ drops from 12.65 to 12.37
• 19 Amps draw measured at B-
• 10.5 volts measured at starter solenoid when grounding to engine block

Ground strap was clearly bad so I replaced it and retested.

Start Attempt 2

• VDrop across the ground strap 0.003v
• B+ drops from 12.68 to 12.32
• 14 Amps at B-
• 11.13 Volts at starter solenoid when grounding to engine block
• Vdrop from B+ to the starter solenoid of 1.3 volts

Clearly the starter solenoid is not closing since if it was the amperage draw would be way higher. It seems clear that the voltage drop between B+ and the positive solenoid terminal is way too high, but is it high enough to prevent the solenoid from engaging? If it is, could it be that the security system switches in a resistor? The Ituran customer service says their remote diagnostics say the system is working correctly.

So one question is why do I have this voltage drop?

Other than bad wiring / connections or a misbehaving anti-theft system, the other explanation I can think of is that high resistance in the ground path put too much stress on the starter solenoid and caused a partial short in it's windings. Could this explain both why it's not engaging and why there is a voltage drop?

So in trying to determine if it's the anti-theft, wiring or starter solenoid that's the problem what would my next step be? I'm thinking maybe get a heavy duty jumper wire and connect directly between the battery and starter solenoid?

Here are some pictures of the old ground strap

and where I'm connecting to measure at the solenoid:

Answer 1

OK, so this turned in an unexpected direction - when I loosened the bolts of the starter some water started running out I when I completely removed it I found this:

Somehow water got into the starter area and the pinion rusted in the extended position. That of course explains why I couldn't hear or feel the solenoid engaging. I took it in to bench test it and it wouldn't move and I got the same readings. It must have been that the solenoid was moving just a tiny bit - enough to make poor partial contact across the terminals.

So I bypassed the solenoid and connected power directly to the motor which was enough to break it free and get it running. Then hooked back up to the solenoid, and it was able to extend and retract the pinion, but I was still getting a voltage drop across the solenoid terminals. So I removed the solenoid, cleaned around it's base where it attaches to the starter body, removed the nuts from the terminals and wiggled things around a bit then put it all back together and walla - no more voltage drop. Spent some time running it on the bench to loosen things up as much as possible, cleaned the mating surface on the starter and the engine with a wire brush, reinstalled and the truck started right up!

Seems what looked like a bad solenoid was a purely mechanical problem...